The invention relates to an electrothermal ignition device for a powder propellant charge. The invention further relates to a method for producing this type of device, as well as a cartridge using the device.
To ignite the propellant-charge powder in known cartridges having an electrothermal ignition device, a high current flows through a wire-type conductor in the floor-side or base region of the corresponding cartridge such that the conductor vaporizes explosively and initiates an arc discharge. This arc discharge then ignites the corresponding propellant-charge powder.
A disadvantage of purely-electrothermal ignition devices is that all of the energy required for a reproducible ignition must be made available electrically, resulting in a considerable requirement of electrical energy.
German Patent Application DE 199 21 379.8, which was not published prior to the present application, discloses that, instead of leading the wire-type conductors directly through the propellant charge, the wires are disposed inside tubes comprising propellant-charge powder. These propellant-charge-powder tubes then constitute ignition conduits inside the propellant charge.
In the activation of the ignition device, first the wire-type conductor vaporizes and an arc-plasma conduit forms inside the respective propellant-charge-powder tubes. Radiation-transport mechanisms transport the energy to the environment via the plasma conduits. This energy transport leads to a rapid ignition of the propellant-charge-powder tubes and their conversion for energy and pressure. The propellant-charge gases formed in the process by the propellant-charge-powder tubes, and the released arc radiation, effect a rapid, uniform ignition of the surrounding propellant-charge structure.
The unpublished document DE 199 21 379.8 also discloses replacing the electrically-conductive wires with a metallization that is applied to the inside of the propellant-charge-powder tubes.
In view of DE 199 21 379.8, it is the object of the invention to disclose an ignition device in which a reduced amount of electrically-supplied energy is required for igniting the powder propellant charge, and with which the advantageous properties of electrothermal ignition can be further utilized. It likewise is the object of the invention to provide a cartridge utilizing the ignition device according to the invention as well as a method for producing this type of ignition device.
The above object generally is achieved according to the invention with regard to the ignition device, by an electrothermal ignition device for igniting a powder propellant charge, comprising: at least one electrically-conductive wire that extends, at least partially, through the propellant charge, and is connectable to a current source; and a pyrotechnical ignition mixture coating the electrically-conductive wire at least in a partial region along its length.
The above object generally is achieved according to the invention with regard to the method, by a method for producing an ignition device as described above that comprises: providing a pyrotechnical ignition mixture that is a mixture on a potassium perchlorate-zirconium (KClO4xe2x80x94Zr) base, and contains a polymer binder from the family of fluoroalkanes; supplying a suitable solvent to the admixture of the binder and the potassium perchlorate-zirconium mixture to produce an emulsion; applying the emulsion to the electrically-conductive wire, and subsequently evaporating the solvent.
Particularly advantageous, modifications and embodiments of the invention are disclosed.
The invention is essentially based on the concept of coating the electrically-conductive wire with a pyrotechnical ignition mixture instead of inserting the electrically-conductive wire into a propellant-charge-powder tube. A mixture on a potassium perchlorate-zirconium (KClO4xe2x80x94Zr) base has proven to be an advantageous ignition mixture.
A polymer binder from the family of fluoroalkanes is preferably added to this mixture. As a result, the ignition mixture can be applied, from a solvent emulsion, to wires, and adheres securely to the wire after the solvent evaporates. The binder component also lends elastic properties to the ignition mixture adhering to the wire.
After the ignition mixture has been initiated by a current flowing through the wire, the mixture is converted; at temperatures of about 4000xc2x0 C., zirconium oxide (ZrO2) is formed, which supports the ignition of the propellant-charge powder as fine hot spots, and reduces the requirement of electrical energy.
Further details and advantages of the invention ensue from the exemplary embodiments explained below in conjunction with drawing figures.